The purpose of this project is to investigate the molecular and cellular basis of the intercellular interactions that control the conjugation response of the yeast Saccharomyces cerevisiae, a relatively simple developmental and morphogenetic sequence. These studies will involve: (a) Elucidation of the mode of action of alpha-factor, the mating-specific oligopeptide pheromone released by alpha haploid cells. Radioactive derivatives and affinity adsorbants prepared from chemically synthesized alpha-factor will be used to identify and purify the alpha cell components that interact with the peptide. (b) Examination of alpha-factor expression. Antibody directed against synthetic alpha-factor will be used to develop a radioimmune assay to screen for mutants defective in normal alpha-factor production and to isolate alpha-factor messenger RNA. This should permit the genetic localization and then the physical isolation of the alpha-factor structural gene(s). (c) Investigation of the role of microtubule synthesis and assembly in the control of the cell division cycle by mating pheromones. The major microtubule protein, tubulin, will be identified. It and heterologous tubulins will be used to isolate nuclear spindle plaques, the in situ organizing center for microtubule assembly in yeast. (d) Characterization of the properties and synthesis of the surface molecules that mediate mating adhesion. Glycoprotein fractions will be isolated from cell walls and plasma membranes and will be tested for their ability to block normal mating-specific agglutination. (e) Selection and examination of mutants defective in various stages of the mating process to aid biochemical analysis of the cellular components involved in the conjugation response and its regulation.